Dichroic coatings are formed by the sequential deposition in alternate layers of materials having high and low refractive indices, each layer being an odd or even multiple of quarter wave length thickness related to monochromatic light of specific wavelength. Thus applied, dichroic coatings reflect certain bands of incident light waves and transmit other bands.
Ideally, the transmission and reflection occurring via a dichroic coating is prefectly controlled by the number of layers used and by the materials used in each of the layers. See for example, U.S. Pat. No. 1,425,967, granted to Hoffman in 1922.
The use of dichroic coatings as "cold" (i.e., heat rejection) mirrors is thus well known. Lamps fabricated with a dichroic coated reflector transmitting substantial amounts of infrared radiation and reflecting substantial amounts of visible radiation have been commercially available for many years, at least since about 1960. Such lamps are widely used in projector applications and as theatrical, television, and movie stage lights.
In contrast to the widely used cold mirrors, lamps may be designed using dichroic coatings to reflect wavelengths other than the visible, e.g., infrared. One such lamp is described in U.S. Pat. No. 4,604,680 (the '680 patent), the disclosure of which is hereby incorporated herein by reference
Getters are materials which entrap extraneous gases. These materials have found wide use in vacuum tubes and high pressure electric discharge devices See for example U.S. Pat. Nos. 3,737,710 and 3,519,864, the disclosures of which are hereby incorporated herein by reference.